Catalyst support material containing lanthanides

ABSTRACT

A catalyst undercoat (wash-coat) material comprising a plurality of stable, highly porous, co-precipitated agglomerated microcrystalline comprised of integral admixture of alumina and at least one lanthanide. The co-precipitated material may be converted to a slurry and used as an undercoat or wash-coat atop a prefabricated low surface area support. Alternatively, the co-precipitated material may be compressed or extruded into various geometric forms and these can be used as a support and as such serve both as the support and the undercoat.

This application is a divisional of application Ser. No. 07/136,279filedDec. 22, 1987, now U.S. Pat. No. 4,868,150.

BACKGROUND OF THE INVENTION

1. Field of the Invention:

The present invention relates to catalytic compositions and methods fortheir preparation and use. More particularly, this invention relates toa catalyst undercoat material useful for providing an undercoat oralternatively a support having a catalytically advantageous pore sizedistribution and high porosity.

2. Description of the Prior Art:

There are many types of wash-coats or undercoats (hereinafter referredto as coatings) as well as solid prefabricated catalyst foundationsknown in the art. It should be noted at the outset that the word supportas used in this application applies primarily to low surface areastructures which serve as catalyst foundations. To this low surface areasupport is applied an undercoat or wash-coat having relatively highsurface area which serves as an anchor or base for the catalytic entityforming the outermost surface of the catalytic composite. Alternatively,the catalyst undercoat material may be compressed or extruded intovarious geometric forms and used directly to support a catalyst. Such asolid may be in a variety of forms including powders, granules, sheets,spheres, extrudates, honeycombs or monolith structures, cylinders orrings, saddles, stars and the like. An example of a material serving asboth a wash-coat and a high surface area catalyst support is aluminawhich is used widely as an undercoat and equally widely in the form ofspheres, cylinders and extrudates of various configurations as a highsurface area support. The undercoat can be thought of as a film of highsurface area applied to a low surface area support to attain highcatalytic activity not otherwise attainable with low surface areasupports.

A variety of high strength low pressure drop catalyst supports are knownin the art. These supports characteristically have a smooth surface andare catalytically inert, non-porous and have a low surface area.

Before a catalyst can be applied to the surface of the support materiala film or layer of high surface area material must first be applied Suchmulti-layer catalysts are frequently used in the chemical industry or inabatement processes for the disposal of combustible or toxic materialsincluding reducing pollutants in waste gases. For example, thesecatalysts may be used for the oxidation of carbonaceous materials aswell as the reduction of nitrogen oxides contained in automobileexhaust.

The current art can be illustrated by the typical catalytic compositecomprising a sturdy foundation illustrated by a low surface areahoneycomb or similar monolithic support. Because this foundationmaterial typically has a smooth surface and is dense and non-porous, afilm or coating of a strongly adherent, refractory, high surface areaand porous nature is applied. It is to this coating that our inventionis directed and will subsequently be fully described. Finally onto andinto this film is applied by impregnation, immersion, spraying or othermeans the catalytic coating comprising oxidation catalysts from theprecious or base metal groups.

Examples of such prior art catalytic composites include those disclosedin U.S. Pat. No. 3,993,572 wherein the catalyst component contains aplatinum group metal, a rare earth metal and an alumina component. Therare earth metal oxides disclosed include cerium, samarium andpraseodymium. The catalyst component may be prepared by co-precipitatingthe ingredients. Such co-precipitation is described as either surfaceabsorption or precipitation of a liquid or solid. The impregnation ofalumina powder with cerium salts is also disclosed.

U.S. Pat. No. 3,867,309 relates to the deposition of palladium and ametal selected from the group consisting of a rare earth, iron,manganese and zinc to high surface area gamma alumina spheres. Anexample of a rare earth or lanthanide is cerium nitrate. Similarly U.S.Pat. No. 3,903,020 describes the impregnation of cerium onto and intoalready formed alumina particles, generally in the form of spheres. Thecerium salt is preferably cerium nitrate. After applying the ceriumnitrate to the surface of the spheres, the entire composite is thencalcined to decompose the lanthanide nitrate and introduce theinterspersed oxide as a stabilizing agent into the alumina.

U.S. Pat. Nos. 3,867,312 and 3,899,444 disclose another procedure whichincludes preparing an aqueous solution of water soluble decomposablesalts of a rare earth metal and a water soluble aluminum salt,evaporating the free water from the solution and then heating theresultant mixture of aluminum salt and rare earth metal salt. A uniformmixture of salts is obtained and subsequently decomposed to relativelylow surface area oxides. The mixed oxides are cooled and a supportmaterial is thus produced. This procedure and slight variations havefound wide application because the decomposition of the nitrate has thedesirable result of producing a comparatively adhesive oxide or mixedoxide. However, the activity of such oxides is very poor because thedecomposition procedure results in an oxide which as noted above is bothdense and low in surface area. Further, these patents are primarilyconcerned with the adhesion of the film and only to a lesser extent, theother physical characteristics. U.S. Pat. No. 3,867,312 refers to theformation of a gel from the precipitation of lanthanum and aluminumhydroxide which gel is then processed into spheres. These spheres becomethe support material for the catalytic coating. No reference is made tothe use of this product as an adhesive film.

While most of the activity in the design of chemical reactions or ofcatalytic abatement processes relates to the development of catalysts,it has become increasingly apparent that the catalytic support materialis itself an important factor in the overall design of the catalyst andthe operating facilities. The catalyst and catalyst bed must be preparedin such a manner as to minimize pressure drop. The current designershave recognized that in order to obtain maximum catalyst performance,the catalyst support or catalyst support surface must be among otherthings rugged and of such a design that the gases or liquids to bereacted will pass through and contact the catalyst deposited on thesurface of the catalyst support material without allowing a substantialpressure drop.

Not only is it necessary that the contact be intimate, but it is alsoessential that the catalyst that is applied to the catalyst support hasa high inherent activity, even when the catalyst is present as a thinfilm on the nonporous surface of a rugged support. This requirementtranslates into a catalytic film having a specific chemical compositionwith a catalytically advantageous pore size distribution, highstability, high porosity and firm adherence to the smooth surface lowpressure drop support.

Thus, while the art has generally recognized the use of a lanthanide forthe stabilization of alumina, there remains a need for highly stablecatalytic support compositions with novel control of total pore volume,pore distribution and thermal stability assuring retention of thesecharacteristics.

The above cited patents are generally representative of the state of theart. From these teachings, it becomes readily apparent that in general awater soluble lanthanide salt or salts are added to some form ofparticulate alumina which is later further processed and ultimatelyapplied as a coating or made into a support in the form of spheres,cylinders, extruded rods and the like. In such preparations, theintimate mixture, high porosity and reproducible physicalcharacteristics taught by the present invention are completely missedbecause either the particulate alumina or lanthanide defeats the needfor co-precipitation herein taught. For example, it is impossible toderive an intimate or integral mixture in unit crystal to unit crystalrelationships by the teachings of the prior art because the crystals inthe particulate portion are massive relative to the trulyco-precipitated materials formed by the practice of the instantinvention.

SUMMARY OF THE INVENTION

It is thus a major objective of the present invention to provide ahighly stable catalyst support material comprising a plurality ofstable, highly porous co-precipitated microcrystalline particulatescomprised of integral admixture of alumina and at least one lanthanide.The catalyst support material may be applied as a slurry to aprefabricated support, thus serving as a wash-coat/undercoat, oralternatively, the catalyst support material may be directly used toproduce a support.

It is another object of the present invention to provide amicrocrystalline or crystallite catalyst support material that isco-precipitated from soluble salts of alumina and at least onelanthanide.

Additionally, it is an object of the present invention to provide acatalyst support material which may have associated therewith a basemetal oxide which is from Group 1B, 3B, 4B, 6B, 7B or 8 of the PeriodicTable.

It is a further object of the present invention to prepare a catalystsupport material which is useful to oxidize gases, in particular, carbonmonoxide and hydrocarbons in automotive exhaust gases.

A still further object of the present invention is a process forpreparing a catalyst support material which has a plurality of stable,highly porous, co-precipitated microcrystalline particulates comprisedof an integral admixture of alumina and at least one lanthanide.

A description of the requirements and basic fabrication techniques for acatalyst to be used in this service is now presented. Because theexhaust from an automotive engine is at very high velocity, thepermissible space velocity and the design of the catalyst for thispermissible velocity is consequently very high. The requirements for thedesign of the catalyst are such that it must take into account the veryhigh space velocity and short contact time. Furthermore, the pressuredrop must be low because the exhaust back pressure from the engine mustbe as low as possible because any back pressure from the catalyst bedwould tend to decrease very substantially the efficiency of the engine.These considerations are important not only for the automotive exhaustabatement systems but also for all abatement systems which are designedfor use in low pressure drop operations. This includes exhaust fromessentially all types of ventilating systems and as well as boilers andflue gas from such steam generating stations for electric and steamgenerating requirements.

THE SUPPORT

The first basic requirement for the support material for the catalyticcomposite is for high rigidity and high strength. This generally means adense, honeycomb type structure with thin, non-porous, almost glassysurfaces. This can be fabricated from many different types ofcompositions with cordierite being most frequently used in theautomotive industry. For other systems there can be metallic, ceramicresembling porcelain, mullite, and the like. Industrial researchersreport that they can make these structures from almost any type ofcomposition. However, for maximum strength, cordierite appears to havethe best overall properties of any existing material. It has an almostglassy and very dense surface.

The support material just described is catalytically essentially inert.However, because many of the catalysts which are supported on it areused at extremely high temperatures, the support material may bechemically quite reactive at these higher temperatures. This may causeharmful solid state reactions between the support and the previouslydescribed wash-coat. Not only can there be a reaction between thesupport and the wash-coat or undercoat, but in severe conditions thecatalytic final coating and the ingredients in the support material maymigrate completely through the wash-coat and damage the final coatingwhich is the active catalyst. It becomes apparent that the ingredientsin the support and the underlayer must be designed to avoid those solidstate reactions to the extent which they can damage the catalystcoating.

THE UNDERLAYER

The underlayer is an important component in the catalyst composite. Itmust have characteristics which make it possible for it to adheretightly to the glassy surface of the support material but simultaneouslyhave a high surface area and high porosity for the retention and activedispersion of the third and final component of the catalytic compositewhich is the catalytic agent itself. It must also prevent solid statereaction between the support and the catalytic coating and not reactharmfully with the catalytic coating. It is to this underlayer that thepresent invention is directed. For this underlayer to function ascompletely as possible for its intended use, it must not only have thecharacteristics already enumerated but because the catalyst may be usedat a high temperature it must also have thermal resistance. Because thecatalyst must be used at very high space velocity, it must also havewell-defined and thermally stable specified pore distribution and totalpore volume. In most cases the catalyst composite will not only be usedin very high space velocity but also at low pressures which means thatthe diffusion of the gases and adsorption of the reactants into and ontothe pores and reactive surfaces must be achieved very rapidly. Thisrequires that the pore distribution be such that there are optimumquantities of large pores for easy diffusion and mass transport but alsothere must be an optimum quantity of small diameter pores where most ofthe catalytic activity and surface adsorption takes place. It is thisthat has been attained by the specific composition and process of thepresent invention. In addition to achieving the desired poredistribution in a bi- or tri-modal regime, it has been discovered thatpowder having the above-enumerated desirable characteristics can be madeto adhere very strongly by further processing the powder and generatinga slurry of paint-like character incorporating colloidal oxides. It isbelieved that this colloidal material also introduces highly desirablelarge pores by properly selecting the particle size of the component orcomponents of the colloid. Attractive catalytic characteristics can alsobe added to the undercoat by selecting the ingredients of the colloid,ceria and other lanthanide oxides being excellent examples.

THE CATALYTIC COMPONENTS

The catalytic composite which consists of the support and theundercoating is fully achieved by adding the third component which isthe catalytic ingredient. These catalytic ingredients are well known inthe art. Useful for this surface catalytic coating are precious metals,particularly platinum, palladium, and rhodium, and certain base oxideswhich are identified in the Periodic Table of the elements in certaingroups. The groups are usually identified as group 8 which includes theprecious metals and individual elements such as manganese, chromium, andcopper as their oxides or interreaction products. These may bestabilized by incorporating high melting point refractories whichinclude alumina, silica, magnesium oxide, calcium oxide, strontium andbarium oxides. A better understanding of the relationship between thesupport, the undercoat, and the catalytic overcoat can be obtained byreference to FIG. 4 which shows in enlarged detail the central componentbeing the support (A), a thin film being the underlayer (B), and a thinovercoat which is the catalytic component (C). The catalytic componentnot only can be a distinct overcoat but in some cases can penetrate intothe undercoat layer itself and become a dispersed material through theundercoat. FIG. 3 is the full-size support and FIG. 5 is an isometricsectional view of one bridge or support of FIG. 4. Other supports suchas spheres, pellets, rods, saddles, rings and the like are well known inthe art.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are an x-ray pattern at 350° C. without aging (2 thetais 4° to 80° ) which shows the crystal peaks of ceria and alumina at aratio of 10%Ce/90%Al, 20%Ce/80%Al and 30%Ce/70%Al.

FIGS. 2A and 2B are an x-ray pattern at 800° C. without aging (2 thetais 4° to 80° ) which shows the crystal peaks of ceria and alumina at aratio of 10%Ce/90%Al, 20%Ce/80%Al and 30%Ce/70%Al.

FIG. 3 is a form of a catalyst support having both an undercoat and acatalytic coating.

FIG. 4 is a cross-sectional view showing in enlarged detail therelationship between the support (A), the undercoat (B) and thecatalytic overcoat (C) of FIG. 3.

FIG. 5 is an isometric projection at a 45° angle of one of the bridgesor supports of FIG. 4.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION

The present invention concerns a catalyst support material comprisingalumina and at least one lanthanide oxide which are co-precipitated fromsoluble salts and which form a microcrystalline, highly stable integralmixture having high porosity and specific bi-modal or tri-modal poredistribution.

The product of the present invention is a microcrystallineco-precipitate. The formation of this fine microcrystallineagglomeration of crystallites is essential when deriving the desirablecontrolled porosity of the present invention. The conglomerate of thepresent invention is also particularly stable, for example, the pores donot collapse at high temperatures and the advantageous surface area,pore volume and distribution are retained.

The lanthanide series metal is present along with the alumina in thecatalyst support material of the present invention as an oxide. Metalsin the lanthanide series include elements having an atomic number from57 through 71, comprising lanthanum, cerium, praseodymium, neodymium,promethium, samarium, gadolinium, terbium, dysprosium, holmium, erbium,thulium, ytterbium and lutetium; preferred are cerium, lanthanum,praseodymium and neodymium. Mixtures of all or part of these, availablecommercially as their salts, may also be advantageously employed. Thelanthanide series elements are most likely to be present in the finallyprepared undercoat in the form of an oxide, peroxide or suboxide.

In the case of automotive exhaust gases, the primary reactions are theoxidation of combustibles to carbon dioxide and water and the reductionof NO_(x) to elemental N₂. These reactions generally occur at elevatedtemperatures, generally in the range of about 100° C. to about 1300° C.,preferably about 100° C. to about 1000° C. but a temperature range ofabout 300° C. to about 400° C. is more common.

The amount of alumina in the catalyst undercoat material may range fromabout 1 to about 75 weight percent based on the total solids contentthereof. The lanthanide oxide may be present in an amount of from about1 to about 45 weight percent based on the total weight of the ceria andalumina therein. Preferably, from about 15 to about 35 percent by weightof lanthanide is used to stabilize the alumina. A catalyst supportmaterial comprised of about 80% alumina and 20% lanthanide is preferred.

The catalyst undercoat material of the present invention is precipitatedfrom water-soluble salts of aluminum and a lanthanide. Suitablewater-soluble salts of aluminum include aluminum nitrate, aluminumsulfate, aluminum chloride, aluminum acetate, aluminum oxalate and thelike. Aluminum nitrate is preferred.

Suitable water-soluble lanthanide salts include cerium nitrate,lanthanum nitrate, praseodymium nitrate, neodymium nitrate, ceriumsulfate, cerium chloride, lanthanum acetate, lanthanum sulfate, ceriumacetate, cerium lactate, cerium propionate, cerium butyrate and thelike. The lanthanide nitrates are preferred since some of the otheranions may unfortunately appear as an occluded ion in the precipitate.For instance, sulfate has a tendency to be occluded and to poison thecatalyst probably as the non-catalytic sulfate or sulfide.

The soluble salts of aluminum and lanthanides are preferably of highpurity. Each of the soluble salts may be prepared by processeswell-known in the art. For instance, aluminum nitrate may be prepared bydissolving pure aluminum metal in dilute nitric acid also of highpurity. Aluminum metal equivalent may represent about 1 to about 50weight percent, preferably about 1 to about 30 weight percent of theentire composition during preparation of the soluble salt.

The total concentration of salts in the aqueous solution prior toco-precipitation generally ranges from about 0.5 to about 1.5 molar,preferably about one molar. The total solids content of the aqueoussolution may be from about 1 to about 20 weight percent, preferably,about 5 to about 10 weight percent. A very broad temperature range issuitable in the preparation of the aqueous solution. A temperature rangeof about 15° C. to about 50° C. is generally used, with 25° C. to 35° C.being preferred.

The co-precipitation of the catalyst undercoat is preferably conductedusing known precipitants. Such precipitants include but are not limitedto ammonium carbonate, ammonium bicarbonate, gaseous ammonia accompaniedby carbon dioxide and the like. Carbonates, bicarbonates and hydroxidesof sodium, potassium or other suitable alkalis may also be used. Theammonium carbonates, however, are preferred since resultant ammoniumnitrate is easily decomposed and leaves the precipitate during calciningwhereas the Na, K, Rb or Cs ions are apt to be occluded and be harmful.

The co-precipitation may be conducted over a temperature range of about15° C. to about 50° C., however, a temperature of about 25° C. to about35° C. is preferred. It is important to control the final pH of theco-precipitation. The final pH of the co-precipitation may be in therange of about 6.0 to about 8.0, more preferably, about 6.7 to 6.9.

The precipitated mixture is washed by decantation if feasible, and/oralternatively, filtered, suspended and rewashed and then filtered, driedand calcined. It may at times be advantageous to leave some of the driedprecipitate uncalcined and to mix it with the calcined material prior tothe undercoat being applied to the support. On calcining this uncalcinedmaterial decomposes providing still more porosity to the coating.

After calcining, if the precipitate has been precipitated with a cationother than ammonium and it is occluded in the calcined precipitate thenthe alkali e.g., sodium, may be removed by ion exchange. The calcinedprecipitate should be washed repeatedly by decantation in an aqueousammonium carbonate or bicarbonate solution at approximately 0.1% to 2%concentration until the offending ion is reduced to an acceptable level.This is generally achieved when only approximately 50 ppm of ion remainsin the precipitate. This is done because alkali adversely affects thephysical and thermal stability of the precipitate.

The precipitated catalyst undercoat of the present invention does notgenerally readily adhere to the support. It has been found that theaddition of a film forming material, for example a colloidal lanthanide,and most preferably colloidal ceria, improves the adhesioncharacteristics of the undercoat to the support. Film forming materials,especially colloidal lanthanide, are available in commerce. The quantityof colloidal lanthanide required to generate the adhesive propertiesused is generally from about 2% to about 40%, preferably about 3% toabout 25% of the total weight of the solids or precipitate. The use ofsuch a colloidal lanthanide is also advantageous because it beneficiallyaffects the activity of the catalyst overlayer. A further benefitderived from the use of colloidal lanthanide is that the largercolloidal particle introduces a still further modification of poredistribution of the composite.

In another embodiment, the slurry of catalyst undercoat and film-formingcolloid, after milling, can be simply dried to a cake which can becrushed and screened for use as granules. Additionally, the slurry canbe dewatered to a paste which can be extruded into appropriate pellets,bars, rods, rings and the like. These structures can be used as suchwithout the foundation support as a satisfactory support for thecatalytic overlayer.

The pore size of the catalyst underlayer of the present invention isunique and important. The pore size of the catalyst should be largeenough to accommodate the eventual catalyst coating and permit the masstransport of the reactants into and out of the pores to allow facileadsorption and reaction in the small functional pores. There are threespecific predominate pore size diameters with the first of those beingbelow about 100 Angstroms, the second being about 200 to 400 Angstromsand the third being greater than about 400 Angstroms. If a plot of poresize versus number of pores indicates a peak in two of those categories,then the pore distribution is bi-modal. If on the other hand, threepeaks, one in each category is obtained, then the pore distribution isconsidered to be tri-modal. Preferably approximately 50 to 60% of thetotal pore volume is less than 200 Angstroms, approximately 20 to 30% ofthe total pore volume is in the 200 to 400 Angstrom range andapproximately 10 to 30% is greater than 400 Angstroms. This quantity oflarge pores provides facile mass transport to the reaction site whereasthe large fraction of small pores provides an abundance of reactionsites. This bi-modal character is considered to be particularlyeffective for automotive emission catalysts.

The surface area of the catalyst underlayer of the present invention ispreferably greater than 50m² /g after treatment at 1000° C. The averagepore volume is preferably in the range of about 0.15 cc/g to about 0.5cc/g.

When a support is used, the catalyst support material of the presentinvention is generally a major amount of the total catalyst structure,typically about 50 to about 80 weight percent, preferably about 50 toabout 65 weight percent, based on the total weight of the catalyst,underlayer and support. The amount used depends on economics, sizelimitations and design characteristics.

These unitary supports are characterized by having a plurality of flowchannels or paths extending therethrough in the general direction of gasflow. During use for oxidation of carbonaceous fuels, the catalyst istypically placed in a vessel so that its structure completely occupiesthe cross-sectional area of the vessel. Advantageously, the structurehas the general shape of the reaction vessel for which it is designed;and when prepared, the catalyst supported on such a structure can beplaced therein with the channels extending in the general direction ofgas flow between an inlet and outlet.

These supports whether of the unitary-skeletal type or pellets arepreferably constructed of a substantially chemically and relativelycatalytically-inert, rigid material capable of maintaining its shape andstrength at high temperatures, for example, up to about 1300° C. Thesupport typically has a low thermal coefficient of expansion, goodthermal shock resistance, and low thermal conductivity. While a supporthaving a porous surface is preferred, the surface may be relativelynon-porous; but in such event it is desirable to roughen the surface toimprove adhesion of deposited compositions.

The geometric, superficial or apparent surface area of the skeletal typesupport including the walls of the gas flow channels is generally about0.5 to 6, and preferably 1 to 5 square meters per liter of support. Thissurface area is sufficient for deposition of a satisfactory quantity ofthe catalyst undercoat of the present invention. The plurality ofchannels, about 100 to 2500, preferably 150 to 500 per square inch ofcross-sectional area, may be distributed across the entire face of thestructure and frequently they define an open area in excess of 60% ofthe total area of the support. The channels generally extend through thesupport and are preferably separated by thin walls. The walls must bethick enough to provide rigidity and integrity to the structure whilemaintaining good available or active catalyst area. The wall thicknessis thus in the range of about 2 to 25 mils. The flow channels can be ofany shape and size consistent with the desired superficial surface areaand should be large enough to permit relatively free passage of thegaseous mixture undergoing reaction.

In order to further illustrate the present invention and the advantagesthereof, the following specific examples are given, it being understoodthat same are intended only as illustrative and in nowise limiting.

EXAMPLE 1 Preparation of Undercoat Containing Alumina and Cerium

A series of precipitations was made to incorporate various ratios ofaluminum oxide and cerium oxide in the range of 0% cerium oxide and 100%aluminum oxide to 100% cerium oxide and 0% aluminum oxide. The ratiostested were 95/5, 90/10, 80/20, 65/35, 50/50, 35/65, 20/80, 10/90, 5/95,and 0/100% respectively. Undercoat of these ratios were all made byco-precipitation of the respective carbonates from the water solublenitrates. The solutions were prepared in such a way so that they wereabout 1.0 molar or less with respect to the combined concentration ofthe nitrates. All precipitations were conducted at about 35° C. usingammonium bicarbonate solution as the precipitant. Supplemental carbondioxide was also added to the reaction mixture and to the slurry duringthe subsequent digestion.

The temperature of precipitation was 35° C. in order to minimize thedecomposition of the carbonate. The carbonate is generally unstable attemperatures above 30° C. The supplemental carbon dioxide was added tomaintain the carbonate at as high of a ratio as possible. When thecarbonate decomposes, there is a tendency for hydroxide formation whichcould produce a less active undercoat upon calcining.

A step by step account of the precipitation and final preparation of theundercoat containing 100% aluminum oxide and 0% lanthanide oxide is asfollows:

1. A solution was prepared at a 1.0 molar level in which about 349 gm ofaluminum nitrate nonahydrate was dissolved in water to make 1 liter ofsolution. Greater quantities or volumes can be made by proportionallyincreasing the aluminum nitrate and the water solution levels.

2. Separately a 20% solution of ammonium bicarbonate was prepared bydissolving the ammonium bicarbonate in sufficient distilled water toattain a 20% solution which is close to the saturation level.

3. The aluminum nitrate solution was heated to 35° C. and was rapidlyagitated.

4. The ammonium bicarbonate solution also at 35° C. was added to thealuminum nitrate solution at such a rate that approximately 1 hour wasrequired for it to reach a pH of 6.9±0.1 pH.

5. The ammonium bicarbonate addition was stopped once a pH of 6.9 wasachieved, however, the carbon dioxide was continued to be spargedthrough the slurry for a period of 1 hour. The temperature wasmaintained at 35° C. during this period.

6. After the period of digestion, the aluminum hydroxide was filteredand washed on the filter with sufficient distilled water to be equal tothe original volume of the slurry. Filtration was generally slow but itcould be improved by recycling some aluminum oxide, which was processedthrough the drying and calcining stages. This previously processedproduct acts as a filter aid in the operation.

7. After filtration the aluminum hydroxide was dried at 150° C. andcalcined at 350° C. for approximately 3 hours. This was the precipitatedaluminum oxide used for comparison in the Examples.

As noted earlier, the forgoing describes a method for the precipitationof alumina alone. However, the same procedure is used in producingundercoats containing alumina and lanthanide oxide.

This example also involves the preparation of an undercoat comprising80% aluminum oxide and 20% cerium oxide. 349gm of aluminum nitrate(nonahydrate) and 30gm of cerium nitrate hexahydrate both dissolved in aliter of solution to form a 1 molar solution. This solution was thenprocessed the same as the procedure previously described in steps 2through 7 above. The resulting co-precipitated cerium oxide-aluminumoxide undercoat was subjected to a number of tests. The undercoat washeated to 1000° C. and thereafter physical measurements were made forX-ray species identification, crystallite size determination and poresize distribution. The catalytic stability and the undercoat's abilityto function as a foundation for catalytic activity was tested byformation of a granular composition on which a small amount of palladiumcatalyst was coated.

FIG. 1 is an x-ray pattern of the undercoat of the present inventionusing 10%Ce/90%Al, 20%Ce/80%Al and 30%Ce/70%Al at 350° C. without aging.

FIG. 2 is an x-ray pattern of the undercoat of the present inventionusing 10%Ce/90%Al, 20%Ce/80%Al and 30%Ce/70%Al at 800° C. without aging.In this figure, 20%Ce/80%Al demonstrates the least surface area loss.The ceria tends to stabilize the alumina from crystallite growth. Thealumina and ceria remain as finely dispersed crystallites or distinctmicrocrystalline particles.

The undercoat was also processed and tested by milling the undercoatprepared above with colloidal ceria or another colloidal lanthanidematerial and then applied as a film to the typical honeycomb ormonoliths used in automotive and other exhaust fume abatement systems.After being placed as a film on the honeycomb, the undercoat wasimpregnated with a small amount of a precious metal specifically 50 ppmof palladium based on the entire weight of the honeycomb (approximately200 ppm based on the weight of the film material itself).

The coated and impregnated monoliths were then tested in a number of gasstreams to determine their effectiveness for abatement of noxious gasestypically present in both industrial and automotive exhaust streams.

Test data for the preparations in this Example are recorded in Table I.

EXAMPLE 2 Preparation of Undercoat Containing Alumina and Praseodymium

The precipitation was made in accordance with Example 1, except thatpraseodymium nitrate was used on the same molar and weight basis as thecerium nitrate of Example 1. Test results for this example areessentially the same as for the results for the 20/80 co-precipitate ofExample 1. The results are recorded in Table I.

EXAMPLE 3 Preparation of Undercoat Containing Alumina and Neodymium

This preparation was identical to that described in Example 1, with theexception that instead of using cerium nitrate, neodymium nitrate wasused on the same molar and weight ratio basis. Test results were verysimilar to those given for Example 1 as recorded in Table I.

EXAMPLE 4 Preparation of Undercoat Containing Alumina and Lanthanum

This precipitation was identical to that of Example 1 with the exceptionthat lanthanum nitrate was used instead of the cerium nitrate on thesame molar and weight ratio basis. Test results were very similar tothose given for Example 1 as recorded in Table I.

EXAMPLE 5 Preparation of Undercoat Containing Alumina and MixedLanthanides

This preparation was also identical to that of Example 1 with theexception that instead of using cerium nitrate, a mixture of lanthanidenitrates was used. This lanthanide salt mixture will vary with the typeof ore being processed by the processing company. The ore used in thisexample contained approximately 50% cerium, approximately 25% lanthanum,approximately 20% neodymium and approximately 5% praseodymium. It alsomay vary for commercial or marketing reasons where certain lanthanidesmay be removed and purified. Thus, the mixture remaining would be devoidof one or more of the normal constituents from the ore.

Usually these preparations with mixtures of lanthanides are more or lessa "shotgun" method of deriving information on the efficacy of individuallanthanides. After the mixture has been evaluated and found to beeffective, individual members in the ore are usually isolated andevaluated to determine the preferred elements. Test results for thismixture are very similar to those of Example 1. The results are recordedin Table 1.

COMPARATIVE EXAMPLE 6

The preparation of the catalyst of this example is typical to that whichis currently used in the automotive exhaust abatement industry. This isthe standard material used today and is the baseline for comparison withthe present invention. This process involves slurrying sufficient ceriumhydroxide and aluminum hydrate or oxide having high-surface area andhigh purity in water. This method is concerned with the addition ofpreformed, pre-precipitated cerium to preformed, pre-precipitatedalumina. Sometimes the alumina is obtained by the hydrolysis of thealuminum alkalies that are intermediates in the synthesis of longstraight chain alcohols. Aluminum hydroxide is a by-product of thishydrolysis. A sufficient amount of these basic ingredients was used toeventually obtain 20% cerium oxide and 80% aluminum oxide. The aluminumhydroxide and cerium hydroxide were placed in a ball mill together withsufficient distilled water so that it could be milled using ceramicballs. Ball milling was continued for approximately 12 hours, and atthis time an impalpable slurry of solids in an aqueous dispersion wasobtained. This was transferred to a glass beaker and sufficient 70%nitric acid was added to dissolve 10 % of each of t he ingredients. Thisslurry was then rapidly agitated and heated to 35° C. Approximately 20%ammonium bicarbonate solution also at 35° C. was immediately added untila pH of 6.9±0.1 was attained. The remaining processes of filtering,drying and calcining were effected as described in Example 1. Availabletest results are given in Table I. The undercoat of the presentinvention had greater porosity and higher thermal stability than theprior art catalyst.

COMPARATIVE EXAMPLE 7

The same procedure was followed as presented in Example 6 above exceptthat the cerium was added as a milled hydrate and the aluminum was addedtotally as water soluble aluminum nitrate. Thus, the cerium was in theform of the commercial cerium product and the aluminum was prepareddifferently. This preparation was processed in a similar manner to thepreceding example. The precipitation was effected with ammoniumbicarbonate and the end point was also 6.9±0.1pH. Filtration, washing,drying and calcining were conducted as described in Example 6. Thisproduct was tested and characterized and the data is summarized in TableI. The cerium hydrate product was not as good as the catalyst materialof the present invention.

COMPARATIVE EXAMPLE 8

The procedure in this example was very similar to that used in Example 7except that the ceria was added as the cerium nitrate and the aluminumoxide was derived from the water insoluble alumina hydrate. Thus, thealumina was in the form of the commercial alumina product and the ceriumwas prepared differently. Once again a 20% cerium oxide and 80% aluminumoxide was produced in the final stage. A milled slurry was prepared andthe milled product was an extremely finely ground slurry as was calledfor in the preceding examples. The slurring, heating and precipitationto a pH of 6.9±0.1, washing, drying, calcining, and evaluation were allconducted in a manner similar to that used in the previous examples withthe activity and physical data also summarized in Table I. This product,is also similar to some products produced by commercial producers ofautomotive fume abatement catalysts. Available data are given in TableI. Poor results were obtained using this catalyst support material aswas the case with Examples 6 and 7.

EXAMPLE 9 Preparation of a Undercoat Containing Alumina and Cerium

A solution was prepared as described in Example 1 to obtain acomposition of 20% cerium oxide and 80% aluminum oxide on a weight basisin the undercoat. Approximately 30 grams of cerium nitrate hexahydrateand 349 grams aluminum nitrate (nonahydrate) were dissolved insufficient distilled water to equal a volume of one liter.

Separately a 20% solution of ammonium bicarbonate was prepared and wasrapidly agitated. The temperature was adjusted to 30° C. A flow ofcarbon dioxide as finely divided bubbles was continuously added to thecarbonate solution during the subsequent precipitation and digestion.

In contrast to the foregoing examples, the aluminum and cerium nitratesolution was added to the rapidly agitated ammonium bicarbonate solutionuntil a pH of 7.0±0.2 was reached. Agitation and carbon dioxide additionwas continued for an additional hour following the completion ofprecipitation. The slurry was filtered, washed on the filter, the filtercake was dried and calcined as described in Example 1. The calcinedpowder was further processed into catalysts as described in point 7 ofExample 1.

The product is characterized in the same manner as previously describedfor surface area, pore distribution, X-ray species identity, crystallitesize and catalytic activity. These data are presented in Table I andTable II.

The data indicates that reverse precipitation produces a very stableproduct. Furthermore, at least 75% of the pore volume is in the 200 to400 Angstrom range compared to less than 50% for the comparativeproducts shown in Examples 6, 7 and 8.

EXAMPLE 10 Characterization of the Undercoats

In this example, all of the preceding materials, the end products ofExamples 1-9, were evaluated for surface area using a Micromereticsanalyzer manufactured by Micromeretics Corporation of Waycross, Georgia.These surface area measurements were recorded in Table I and after heattreatment of 1000° C.

The preceding materials were also examined for total pore volume, poredistribution and for catalytic effectiveness. The data are reported inTable I.

In Example 1, particularly the preparation containing 20% CeO₂ and 80%Al₂ O₃, the total pore volume was 0.210 ml/gram whereas the poredistribution was roughly 50-60% less than 200 Angstroms; 20-30% in therange 200-400 Angstroms and 10% greater than 400 Angstroms. This is aparticularly preferred or optimum distribution of pores for anundercoat.

The activity of this composition even without precious metals isapproximately 90% oxidation of CO and C₃ H₆ at 300° C.

Example 9 prepared from the same ingredients by co-precipitation butwith the reverse order of precipitant addition gave the followingcharacterization data:

Approximately 0.40 ml/gram total pore volume after heat treatment at350° C. only 0.15 ml/gram after heat treatment at 1000° C. After heattreatment at 1000° C., the distribution was 15% less then 200 Angstroms,20% between 200 and 400 Angstroms and 65% greater then 400 Angstroms.This does not meet the most preferred characteristics of the invention,even though co-precipitated, but is better than any of the products ofthe prior art.

Example 6, 7 and 8 represent preparations of the prior art and each hadtotal pore volume at least 23.8% below that of the 80% alumina/20% ceriaresults of Example 1. The pore distribution was sharply different withonly about 15-25% being less then 200 Angstroms, roughly the same amountbeing 200-400 Angstroms. In all three instances, the total percentage ofpores greater than 400 Angstroms exceeded the percentage of pores under400 Angstroms. This is in stark contrast with the undercoat of thepresent invention. It will be noted also that the catalyst activity wasonly about 60% of that of the product of the present invention.

EXAMPLE 11

Additional samples of the aluminum oxide-cerium oxide were prepared andafter calcining at 1000° C. for two hours, were examined by X-raydiffraction for crystallite size. The objective was to determine whichcomposition resisted crystallization to the greatest extent. Minimizingcrystal-lite growth is important to obtain greatest retention ofinherent catalyst activity. The samples prepared were as follows:

A. A lot prepared as in Example 1 and with an Al₂ O₃ :CeO₂ ratio of90:10.

B. A lot prepared as in Example 1 and with an Al₂ O₃ to CeO₂ ratio of80:20.

C. Mixed products of Example 1 comprising 1.5 part of 100% precipitatedAl₂ O₃ and 1 part of a 50:50 co-precipitate of cerium oxide and aluminumoxide milled together for 12 hours to obtain a homogeneous product. Thisproduct comprising a mixture of precipitated Al₂ O₃ and aco-precipitated cerium carbonate and aluminum hydroxide with a Al₂ O₃ toCeO₂ ratio of 80:20 was dried then calcined at 1000° C.

D. A mixture similar to 11-C except the 80:20 Al₂ O₃ :CeO₂ product wasobtained by milling together separately precipitated Al(OH)₃ andCe(OH)₃. This also was heated to 1000° C. and maintained at thistemperature for 2 hours.

E. An additional 20:80 CeO₂ :Al₂ O₃ was obtained by milling together for12 hours 3 parts precipitated aluminum oxide and 1 part of a 20:80co-precipitated Al₂ O₃ :CeO₂. This was also calcined at 1000° C. for 2hours.

F. An 80:20 Al₂ O₃ :CeO₂ mixed product was made by a procedure similarto that used as the undercoat (wash-coat) of commerce. Sufficient ceriumhydroxide of the type sold by Rhone-Poulenc Company and aluminum oxidedesignated Catapal sold by Vista Chemicals, Inc. was milled together for12 hours to produce an 80:20 Al₂ O₃ to CeO₂ mixture on final calcining.After milling the slurry was acidified with sufficient nitric acid toconvert approximately 10% of the mixed oxides-hydroxides to nitrate.This product was also calcined at 1000° C.

The six samples and the product of Example 9 after calcining at 1000° C.were examined by X-ray spectrometer to determine stability (resistanceto crystallite growth). The data were recorded in Table II.

The data in Table II indicates that Example 11-B is the most stable andmost active. The stability is illustrated by the fact that after 1000°C. calcining the crystallite of both the CeO₂ and Al₂ O₃ remainrelatively low. Examples 11-C, 11-D and 11-E indicate thatco-precipitation and subsequent mixing is inferior to 100%co-precipitation. Sample 11-F is the typical product of commerce and itscatalytic inferiority is suggested by the excessive crystallite growthduring 1000° C. calcining.

Table II describes a co-precipitated undercoat comprising alumina andcerium oxide which after calcining 1000° C. has ceria crystallites of atwo theta angle at 32.9° which do not exceed 90 Angstroms in diameterand preferably do not exceed 75 Angstroms in diameter. Also described isa co-precipitated undercoat comprising alumina and lanthanum oxide whichafter calcining at 1000° C. had a lanthanum crystallite size that didnot exceed 75 Angstroms in diameter.

                                      TABLE I                                     __________________________________________________________________________                                                C.sub.3 H.sub.6                                                                   NO.sub.x                                      Surface                                                                            Total Pore        CO Oxd.                                                                            Oxid.                                                                             removal                                                                            Pal- Crystal-            Alumina                                                                            Lanth-                                                                              Heat Area Vol.      >200    at   at  300° C.                                                                     ladium                                                                             lite                %    anide %                                                                             Treat.                                                                             m.sup.2 /g                                                                         ml/g  <200Å                                                                         <400Å                                                                         >400Å                                                                         300° C.                                                                     300° C.                                                                    Zero O.sub.2                                                                       Content                                                                            Size                __________________________________________________________________________                                                              Å               Example 1                                                                     All soluble salts                                                             100   0 CeO.sub.x                                                                        1000° C.                                                                    69    0.163                                                                              0.10051                                                                           0.0449                                                                            0.0176                 296                 95    5 CeO.sub.x                                                                        1000° C.                                                                    77                                                            90   10 CeO.sub.x                                                                        1000° C.                                                                    62    0.132                                                                              0.0915                                                                            0.0281                                                                            0.0176                                                                            81.7%                                                                              66.9%                                                                             25.0%                                                                              50                                                                                 142                 80   20 CeO.sub.x                                                                        1000° C.                                                                    86    0.202                                                                              0.1231                                                                            0.058                                                                             0.0213                                                                             89.67%                                                                            87.9%                                                                             27.6%                                                                              50                                                                                 190                 65   35 CeO.sub.x                                                                        1000° C.                                                                    72    0.180                                                                              0.113                                                                             0.047                                                                             0.020                                      50   50 CeO.sub. x                                                                       1000° C.                                                                    51    0.172                                                                              0.1397                                                                            0.0199                                                                            0.0123                 218                 35   65 CeO.sub.x                                                                        1000° C.                                                                    41    0.115                                                                              0.075                                                                             0.028                                                                             0.0121                 218                  0   100 CeO.sub.x                                                                       1000° C.                                                                     9    0.012                                                                              0.0075                                                                            0.0018                                                                            0.0029                 553                 Example 2                                                                     Soluble                                                                            Soluble                                                                  Salt Salt                                                                     80   PrO.sub.x                                                                           1000° C.                                                                    82   0.28  0.15                                                                              0.073                                                                             0.057                                                                             87.3%                                                                              89.4%    27.0%                                                                               50 ppm                  20                                                   185                 Example 3                                                                     Soluble                                                                            Soluble                                                                  Salt Salt                                                                     80   NdO.sub.x                                                                           1000° C.                                                                    79   0.27  0.15                                                                              0.065                                                                             0.045                                                                             86.4%                                                                              88.6%    31.6%                                                                               50 ppm                  20                                                   169                 Example 4                                                                     Soluble                                                                            Soluble                                                                  Salt Salt                                                                     80   LaO.sub.x                                                                           1000° C.                                                                    81   0.28  0.16                                                                              0.065                                                                             0.55                                                                              84.1%                                                                              84.5%                                                                             28.4%                                                                              50                                                                                 173                      20                                                                       Example 5                                                                     Soluble                                                                            Soluble                                                                  Salt Salt                                                                     80   Mixed 1000° C.                                                                    80   0.23  0.13                                                                              0.05                                                                              0.05                                                                              89.8%                                                                              89.2%                                                                             30.5%                                                                              50                                                                                 183                      Lanth-                                                                        anides                                                                        20                                                                       Example 6                                                                     Soluble                                                                       Salt  Solid                                                                   80   Ce(OH).sub.4                                                                        1000° C.                                                                    64   0.16  0.03                                                                              0.03                                                                              0.10                                                                              68.2%                                                                              63.4%                                                                             10.4%                                                                              50                                                                                 206                      20                                                                       Example 7                                                                     Soluble                                                                       Salt Solid                                                                    80   Ce(OH).sub.4                                                                        1000° C.                                                                    67   0.15  0.04                                                                              0.03                                                                              0.08                                                                              59.4%                                                                              64.4%                                                                             12.6%                                                                              50                                                                                 201                      20                                                                       Example 8                                                                          Soluble                                                                  Solid                                                                              Salt                                                                     Al(OH).sub.3                                                                       20    1000° C.                                                                    58   0.13  0.02                                                                              0.04                                                                              0.07                                                                              51.0%                                                                              39.4%                                                                             11.9%                                                                              50                                                                                 196                 80                                                                            Example 9                                                                     Soluble                                                                            Soluble                                                                  Salt Salt                                                                     80   20    1000° C.                                                                         0.15  0.02                                                                              0.03                                                                              0.10                                                                              85.7%                                                                              86.2%                                                                             16.6%                                                                              50                       __________________________________________________________________________                                                         ppm                  

                                      TABLE II                                    __________________________________________________________________________    Heat                  Crystallite                                             Treatment   Prepared                                                                            Al.sub.2 O.sub.3 :                                                                Size    Ceria 2 Theta 32.9                              Example                                                                            Temperature                                                                          By    CeO.sub.2                                                                         CeO.sub.2                                                                         Al.sub.2 O.sub.3                                                                  Crystallite Size                                __________________________________________________________________________    11-A 1000° C.                                                                      Co-prec                                                                             90:10                                                                             1024                                                                              570 58.4                                            11-B 1000° C.                                                                      Co-prec                                                                             80:20                                                                             1222                                                                              304 60.19                                           11-C 1000° C.                                                                      Co-prec +                                                                           80:20                                                                             1892                                                                              786 80.71                                                       Mix                                                               11-D 1000° C.                                                                      Co-prec +                                                                           80:20                                                                             1560                                                                              777 138.0                                                       Mix                                                               11-E 1000° C.                                                                      Co-prec +                                                                           80:20                                                                             2221                                                                              469 79.4                                                        Mix                                                               11-F 1000° C.                                                                      Purchase                                                                            80:20                                                                             2345                                                                              309 107.45                                                      Mix                                                               9    1000° C.                                                                      Reverse                                                                             80:20                                                                             1289                                                                              353 66.08                                                       Co-prec                                                           __________________________________________________________________________

While the invention has been described in terms of various preferredembodiments, those skilled in the art will appreciate that variousmodifications, substitutions, omissions, and changes may be made withoutdeparting from the spirit thereof. Accordingly, it is intended that thescope of the present invention be limited solely by the scope of thefollowing claims.

What is claimed is:
 1. A method of oxidizing or reducing gasescomprising contacting said gases at an elevated temperature of about100° C. to about 1300° C. with a catalyst support material comprising aplurality of stable, highly porous, co-precipitated microcrystalliteparticulates consisting essentially of an integral admixture of aluminaand at least one lanthanide oxide, wherein said lanthanide oxidecomprises at least 1% cerium oxide, and wherein about 20 to 30% of thepores have a pore diameter within the range of about 200 to 400Angstroms.
 2. The method as claimed in claim 1 wherein said gases arepresent in internal combustion engine exhaust.
 3. The method as claimedin claim 2 wherein said gases are carbon monoxide and hydrocarbons. 4.The method as claimed in claim 1 wherein said catalyst support materialhas an active catalyst deposited thereon.
 5. The method as claimed inclaim 1 wherein about 50 to 60% of the pores on the catalyst supportmaterial have a pore diameter of less than 200 Angstroms.
 6. The methodas claimed in claim 1 wherein the lanthanide oxide is an oxide of ceriumand at least one member of the group consisting of lanthanum,praseodymium, neodymium or mixture thereof.
 7. The method as claimed inclaim 1 wherein the amount of alumina is from about 1 to about 75 weightpercent of the entire solids content of the catalyst support material.8. The method as claimed in claim 7 wherein the lanthanide oxide ispresent in an amount of from about 1 to about 45 weight percent based onthe weight of the alumina in the catalyst support material.
 9. Themethod as claimed in claim 1 wherein said catalyst support materialfurther comprises a film forming material.
 10. The method as claimed inclaim 1 wherein said catalyst support material is provided as a coatingon a support.
 11. A method of oxidizing or reducing gases comprisingcontacting said gases at an elevated temperature of about 100° C. toabout 1300° C. with a catalyst support material comprising a pluralityof stable, highly porous, co-precipitated microcrystallite particulatesconsisting essentially of an integral admixture of alumina and at leastone lanthanide oxide, wherein said lanthanide oxide comprises at least1% cerium oxide, and wherein said average pore volume after calcinationis in the range of about 0.15 cc/g to about 0.5 cc/g.
 12. The method asclaimed in claim 11 wherein said gases are present in internalcombustion engine exhaust.
 13. The method as claimed in claim 12 whereinsaid gases are carbon monoxide and hydrocarbons.
 14. The method asclaimed in claim 11 wherein said catalyst support material has an activecatalyst deposited thereon.
 15. The method as claimed in claim 11wherein about 50 to 60% of the pores on the catalyst support materialhave a pore diameter of less than 200 Angstroms.
 16. The method asclaimed in claim 11 wherein the lanthanide oxide is an oxide of ceriumand at least one member of the group consisting of lanthanum,praseodymium, neodymium or mixture thereof.
 17. The method as claimed inclaim 11 wherein the amount of alumina is from about 1 to about 75weight percent of the entire solids content of the catalyst supportmaterial.
 18. The method as claimed in claim 17 wherein the lanthanideoxide is present in an amount of from about 1 to about 45 weight percentbased on the weight of the alumina in the catalyst support material. 19.The method as claimed in claim 11 wherein said catalyst support materialfurther comprises a film forming material.
 20. The method as claimed inclaim 11 wherein said catalyst support material is provided as a coatingon a support.